The present application relates to magnetic resonance (MR) imaging and spectroscopy. It finds particular application transmit and receive coil systems for use with MR systems, and also to cryogenic coils for the MR examination of animals.
MR examination techniques have proven to be a valuable technique for obtaining information about the internal structure and function of an object under examination. A particularly successful application of MR has been the clinical imaging of humans. Still another application for MR is so-called pre-clinical imaging, in which mice, rats, and other small animals are imaged in connection with ongoing medical research. Information from such research can, in turn, be used to develop potentially life-saving treatments for use with human patients.
One limitation on the utility of the images and other information generated by MR scanners is the effect of electrical noise. Indeed, signal to noise ratio (SNR) is a key parameter used to evaluate the quality of the information generated by an MR scanner.
Various techniques have been used to improve MR system SNR. As increasing the strength of the main magnetic field increases the quality of the resultant MR signals, there has been an ongoing trend toward the use of scanners having ever higher field strengths. However, systems incorporating higher field strength magnets are generally more complex, larger, and more expensive than lower field strength systems. Additionally, their sensitivity to certain forms of artifacts may rise with rising magnetic field strength such that the optimum solution may in some cases lie in the highest SNR study at the lowest possible field strength. Even for a system operating at a given field strength, however, it remains desirable to provide a relatively higher SNR.
Cryogenic RF receive coils have been used to improve MR system SNR. These coils have been implemented using high temperature superconductor (HTS) material or cold copper (i.e., copper or oxygen free copper coils cooled near to or below liquid nitrogen temperatures) to both reduce the coil resistance and thermal noise. While cryogenic coils have favorable noise characteristics, they tend to be relatively larger and more complex than comparable warm coils.
At the same time, pre-clinical and small animal applications can present their own set of challenges. For example, animal scanners tend to have relatively smaller imaging regions than those of scanners designed for use with larger objects, such as humans. As a result, the space available for the RF coils and animal handling components is typically rather limited. These geometric considerations also complicate coil system positioning and animal handling.
Still another factor is the variety of MR scanners and applications. For example, MR scanners are available at a variety of main magnetic field strengths. As the Larmor frequency of the MR active nuclei under examination is a function of the field strength, the RF coils must be tuned for use at the desired field strength. Even at a given field strength, various applications may require the examination of different MR active nuclei or the use of RF coils having different fields of view or other performance characteristics. Accordingly, it is desirable to provide coil systems which can readily accommodate these varying requirements.